This invention relates to a process of dressing contaminated soils, which as an aqueous slurry are agitated in a drum, whereafter the effluent from the drum is separated into relatively coarse and relatively fine fractions.
The decontamination of soils or dumps which have been contaminated by hydrocarbons, oils or heavy metals is highly expensive. For this reason it has been proposed to separate such soils by dressing into a fraction which is not contaminated or only slightly contaminated and into a fraction in which a major part of the polluants is concentrated. That fraction can then be decontaminated by methods which are simpler and much less expensive.
From J. E. Garnett, D. L. Mitchell, P. T. Faccini "Initial Testing of Pilot Equipment for Soil Decontamination", REP-3022, TIC-4500, DE-AC 04-76D P03 533, U.S. Department of Energy, Oct. 17, 1980, it is known to subject soils which are contaminated with plutoniumladen oil by wet dressing. The plutonium is associated with the fine-grained particles of the soil, which are separated from the coarser particles. The soil is first treated in a drum washer, in which dry aggregates are broken up and oil is removed by washing from gravel and coarse sand. Washing is effected with an aqueous NaOH solution at pH 11. The drum is provided with small blades for an improved agitation of the slurry. At its discharge end, the drum is provided with a sieve, which retains about 50% as an oversize above 4 mm. The undersize is sieved on a sieve which has a sieve cut of 0.5 mm and on which the +0.5-mm fraction is retained. The -0.5-mm fraction is subjected to hydrocyclonic and centrifugal separation into a +0.05-mm fraction and a -0.05-mm fraction. The -0.05-mm fraction is flocculated and centrifugated for effecting a separation into solids and washing liquor. The latter is recycled to the drum washer and the sieves. But that process has not effected a satisfactory decontamination of the soil.